1. Field
In communication systems, for example Long Term Evolution (LTE) of the 3rd Generation Partnership Project (3GPP), various ways of configuring a short scheduling request (SR) cycle may be able to add flexibility for a network (NW) to configure scheduling request cycles.
2. Description of the Related Art
Release 8 (Rel-8) of Long Term Evolution (LTE) of the 3rd Generation Partnership Project (3GPP) provides two scheduling request (SR) mechanisms: dedicated periodic scheduling requests resource on a physical uplink control channel (PUCCH) configured by radio resource control (RRC) and signaling and a scheduling request sent via random access. The latter is only allowed (in Rel-8) if dedicated scheduling request resources are not configured or transmissions on the dedicated scheduling request resources fail repeatedly.
Background type traffic can be considered, for example, to be user equipment (UEs) that infrequently generate/receive small amounts of data. The interarrival time of such traffic can be in the order of several seconds or several 10 s of seconds and the amount of data to be sent can be in the order of 50-150 bytes.
Background traffic user equipment, therefore, may be allocated less frequent scheduling request resources on a physical uplink control channel. Long scheduling request cycles produce latency of uplink transmissions, as user equipment have to wait for the next scheduling request resources to indicate to an evolved Node B (eNB) that the user equipment has some data to transmit. The extra latency may have less impact at the beginning of a data session and more during a data session.
Discontinuous reception (DRX) in LTE is specified such that when a user equipment receives either downlink (DL) assignment or uplink (UL) grant on a physical downlink control channel (PDCCH), the user equipment (re)starts an inactivity timer during which the user equipment monitors the physical downlink control channel for further uplink or downlink allocations. Furthermore, after the inactivity timer expires, the user equipment uses a short discontinuous reception cycle (if configured) for a given time (discontinuous reception short cycle timer) before entering a long discontinuous reception cycle again. Thus, downlink physical downlink control channel monitoring adapts to data transmission activity.
The same is not true for periodic scheduling requests. Periodic scheduling requests are simply configured by radio resource control signaling to a (semi-)static value, which can only be changed via radio resource control reconfiguration.
The extra latency for uplink can have an impact when some data is sent in the downlink direction, which should be acknowledged in the uplink direction (for example, transmission control protocol (TCP) acknowledgment (ACK)). Delay of acknowledgment can reduce the data rate in the downlink.
To summarize, currently discontinuous reception (for downlink physical downlink control channel monitoring) adapts with data activity (long and short discontinuous reception cycles and inactivity timer) but uplink scheduling requests can only be “adapted” via radio resource control signaling.
More particularly, periodic scheduling request resources can conventionally be configured via radio resource control signaling either for small latency (for example, scheduling request resource every 5 ms) or for less resource consumption (for example, scheduling request resource every 80 ms). Alternatively, a random access (RA) based approach can be used (if periodic scheduling request resources are not configured). Random access, however, can increase load and thus collisions on the random access channel (RACH).
Thus, conventionally, an uplink scheduling request cycle can only be adapted using radio resource control signaling. This approach, however, can either lead to increased latency and/or use of extra resources for, for example, background type traffic.